Asphaltic compositions useful for building of roadways, driveways and the like are well known and in addition to the bituminous material therein contain aggregates in order to increase the strength and long life of such surfaces.
One problem that has long existed with such asphaltic compositions containing aggregate has been the inability to get the desired degree of adhesion of the asphaltic materials to the aggregate; it tends to strip away from the aggregate. In fact this problem is so well known that certain materials added to ameliorate this problem are referred to as "antistrip" materials. A great deal of work has been done in order to prevent the asphalt from stripping away from the aggregate which leads to raveling, loss of aggregate, and other deterioration of the paved surface, particularly under the rigors of heavy traffic.
At the present time a variety of different materials are added as antistripping agents and these include lime as well as a variety of lignins and amine compounds. Even these materials do not satisfactorily operate to give the necessary antistrip characteristics required.
Various efforts to improve adhesion are detailed in patents such as U.S. Pat. Nos. 2,582,823 and 2,582,824 to Fowkes in which the amine type of antistripping agents or the use of acids and soaps, as well as the use of lime, are discussed and their disadvantages noted. In an attempt to improve these well-known problems, with respect to cut-back asphaltic compositions, there is disclosed a priming solution to be used to attain this better adhesion. For this purpose Fowkes discloses using alkaline metal salts of certain inorganic acids to form a wet aggregate which is admixed with the cut-back asphalt. Such priming solution does not give the necessary adhesion, does not work with all types of aggregates, and does not work satisfactorily with hot-mix asphaltic compositions. Under the press of heavy traffic the resultant compositions crack and lose whatever alleged antistripping function they possess.
U.S. Pat. No. 2,469,728 describes another effort to improve the adhesion of the asphalt to the mineral aggregate consisting of mollusk shells in which the shells are first treated with a dilute solution of a strong mineral acid and the thus treated aggregate then coated with asphalt. Here again, such is limited to a cut-back asphalt as set forth in column 1.
It has not heretofore been possible to provide a satisfactory additive for asphaltic compositions; particularly hot-mix asphaltic compositions, which would not only react with the conventional amine antistrip materials utilized, but which will form salts with the amines which are highly water and oil insoluble, and bond effectively with all aggregates utilizable in asphaltic compositions.